<pre># Create dictionary with segmentid as key, calculated length as value1, measured length as value2
fiberCableLengths = defaultdict(list)
with arcpy.da.SearchCursor(fiberCable, ['segmentid', 'calculatedlength', 'measuredlength']) as cursor:
    for row in cursor:
		fiberCableLengths[row[0]].append(row[1])
		fiberCableLengths[row[0]].append(row[2])
		
# Create slackloop dictionary with segmentidfkey as key, total up the length values of each slackloop under that segmentidfkey, and store as the dictionary value
slackloopLengths = defaultdict(list)
with arcpy.da.SearchCursor(slackLoop, ['segmentidfkey', 'length']) as cursor:
    for row in cursor:
		if row[1] is not None:
			slackloopLengths[row[0]].append(int(row[1]))
	
sumValueDict = {k: sum(v) for k, v in slackloopLengths.items()}
	
# For each fibercable segmentid in dictionary, If calculated length + total slackloop length = measured length – Add to good list, Else – Add to bad list
goodList = []
badList = []
with arcpy.da.SearchCursor(fiberCable, ['segmentid', 'calculatedlength', 'measuredlength']) as cursor:
    for row in cursor:
		for k, v in sumValueDict.items():
			if row[0] == k:
				if row[1] and row[2] is not None:
					if int(row[1]) + int(v) == int(row[2]):
						goodList.append(str(row[0]))
						print "Good List: " + row[0]
						print int(row[1]) + int(v)
						print int(row[2])
					else:
						badList.append(str(row[0]))
						print "Bad List: " + row[0]
						print int(row[1]) + int(v)
						print int(row[2])
print "Good List Size: " + str(len(goodList))
print "Bad List Size: " + str(len(badList))</pre>

The code above creates a dictionary where each item looks like the following:
```'1f169eae-5d7c-4ebb-90cd-abbe0e1b72dd': [50.0, 50.0, 50.0, 50.0]```

**How do I get it to sum the values for each key?** The output I'd be looking for here would be:
```4ebb-90cd-abbe0e1b72dd': [200]```

Resources I've looked at:

https://stackoverflow.com/questions/4880960/how-to-sum-all-the-values-in-a-dictionary/4881100
https://stackoverflow.com/questions/34849651/how-to-add-the-values-of-dictionary-with-same-keys-in-python
https://stackoverflow.com/questions/34849651/how-to-add-the-values-of-dictionary-with-same-keys-in-python